A major strength of the Program is the integration of changes in gene regulation with mouse models of cancer and relating these results to human cancer. The overall goals of the current Program is to investigate the roles of both short and long non-coding RNAs in the development of cancer and the importance of the Rb-E2F pathway in cell death and malignancy. miRNAs probably interact with half of all mRNAs, suppress the level of expression of most of these mRNAs by less than two fold, and yet clearly modulate the development of cancer in mouse models. These small RNAs regulate growth and cell death genes, both modulators of tumor growth, and they also shape developmental transitions. The first Overall Aim of the Program is to Investigate the effects of loss of miRNA functions on cell viability, developmental processes and the development of malignancies. The three projects are investigating the general roles of miRNAs in gene regulation including their mechanisms of action, the consequence of loss of all miRNAs in Dicer null cell lines, and the relationship between miRNAs and differentiation of mesenchymal tumors and stem cells. Targeted mouse genetics will be used to investigate the roles of miRI43-145 cluster in development and tumor suppression. This will involve exploration of the effects of activation of this family of miRNAs in tumors in vivo. The second Overall Aim is to Explore the roles of other types of non-coding RNAs in normal and malignant cells. The population of non-coding RNAs will be characterized in Dicer null and tumor cells in search of RNAi-related transcriptional regulation. This includes further investigation of possible Argonaute functions in the nucleus and the roles of non-coding RNAs generated from most promoters by divergent transcription. The large intervening non-coding RNAs (lincRNAs) regulated by p53. and their roles in tumor biology will be investigated using targeted mouse genetics. The third Overall Aim is to investigate the interactions of tumor suppressor genes Rb and p53 and non-coding RNAs in control of cancer and the plasticity of the differentiation state of cells. The relationship of line RNAs and p53 and of Rb and miRNAs in developmental transition and in maintaining cell state will be investigated. The interactions and involvement of Rb and miRNAs in induction of cell death following DNA damage will also be studied.